Can I Delete the JSON Files From Google Takeout?
Yes, but only after you have used them. The .json files hold your photo dates and locations. Delete them first and that information is gone for good.
Yes, but the order matters more than anything else on this page.
Those .json files are not junk that Google shipped by accident. They hold the capture date, the location, your captions and your album information, for every photo that does not carry that data inside it. Delete them while your photos are still blank and you have thrown the information away. Running Takeout again is the only way back, and that means waiting days for another export.
So the safe order is: merge first, check a few photos by hand, then delete the sidecars. Once the dates and GPS are written into the pictures themselves, the .json files have nothing left to give and you can clear them out. One exception: if you are importing into Immich or PhotoPrism, keep them until that import has finished, because those tools read the sidecars directly.
Merging is the easy part. The app reads every sidecar, writes the real date and location into each photo, and reports which files it could not match. Then you can delete the .json files knowing nothing was left behind. The first 500 photos are free.